Recovery of tin and other oxidizable metals



Patented Jan. 31, 1939 UNITED STATES RECOVERY OF TIN AND OTHER OXIDIZABLE METALS Hartmut W. Richter, Rahway, N. J.

No Drawing.

Application January 28, 1936,

Serial No. 61,174

15 Claims.

My invention relates to the separation of tin and other oxidizable metals such as lead, antimony, arsenic, etc., from alloys or materials containing the same and particularly to improve methods for this purpose from which the recovery of metals is relatively high and in which the time required and the operating costs are relatively W.

It has been the practice in accordance with one method heretofore employed in the purification of lead alloys, wherein tin is also recovered, to melt the alloy and treat the same while molten with a strong alkali and an oxidizing agent. However, this method is not adapted for use in the treatment of materials such as slimes obtained in electrolytic processes. Moreover, when alloys treated in this way contain antimony, the lead will not dissolve until the dissolution of the antimony has been completed. Furthermore, when caustic soda is used as the alkali, the antimony combines to form the water insoluble sodium antimoniate which is not readily separated from the material being treated or from other substances which may precipitate.

It has also been proposed to treat tin and lead bearing alloys by heating or boiling the same with a solution of caustic soda containing sodium nitrite or sodium chromate or di-chromate as the oxidizing agent, but this method also is not applicable to the treatment of many materials and in some cases requires prolonged treatmentbefore substantial recovery of the tin or lead can be efiected. Furthermore, sodium nitrate or other nitrates which are cheaper than the corresponding nitrites cannot be used in the process. This is presumably due to the fact that the nitrates do not undergo such ready decomposition as the nitrites and therefore do not enter into the reaction at the temperatures attained in such operations.

I have discovered that these disadvantages of prior art methods can be overcome and the recovery of tin, lead, antimony and arsenic can be effected very readily by treating alloys or 45 other materials containing these metals with an alkali and an oxidizing agent under such conditions that the temperature is carried considerably above that employed when the material is boiled with an alkali solution but well below the melting point of the alloys or metals to be recovered. I have found that under these condi-' tions the materials react very satisfactorily and since the reagents are present in a concentrated and very effective form the amount thereof required may frequently be considerably reduced while the recovery of tin from the material may be increased.

All of the materials may be used in a dry form so that the reaction is carried out in a dry way or the alkali or oxidizing agent, or both, may be 5 used in molten form. l

The reagents may also be used in the form of a solution. However, in such cases the water which is present, or added in carrying out the reaction, should not exceed that which will be 10 driven off or decomposed as the reaction continues, so that a dry or substantially dry reaction mass is obtained from which the materials to be recovered may be leached or otherwise separated.

Although my invention is particularly applicable to the recovery of tin from materials containing the same, it may also be used for the recovery of other metals such as lead, antimony and arsenic, and may be used in treating mate- 20 rials containing one or more of the latter metals even when tin is not present or when it is present only in small amounts. Furthermore, materials may be treated to recover all of the lead present therein while a substantial part of the 25 antimony which is oxidized during the reaction is converted to a water soluble compound that may be readily separated and recovered. The latter feature of my process is of particular importance in the treatment of materials contain- 30 ing a large amount of copper, since a high grade copper concentrate substantially free from lead and antimony may be produced.

One of the objects of my invention is to provide an improved method for the recovery of tin 35 and/or lead, antimony and arsenic from alloys or materials containing the same.

Another object of my invention is to provide a process whereby tin, lead, antimony and arsenic may be extracted from materials and obtained 40 in water soluble form.

A further object of my invention is to reduce the time and cost of treating alloys or materials containing tin, lead, antimony and arsenic and to increase the amount of the metals recovered.

Another object of my invention is to provide a method adapted for use in the recovery of tin and other metals which is applicable for use in the treatment of a great variety of materials and wherein the oxidizing agent employed may be a so nitrate.

Another object of my invention is to provide a process for the recovery of tin and other oxidizable metals from materials containing the same wherein a dry reaction product is produced. w

A further object of my invention is to provide a process whereby materials containing tin, lead, antimony, and arsenic can be treated in a dry way to eifect the recovery of these metals.

These and other objects and features of my invention will appear from the following description thereof in which examples are cited to represent typical procedure in accordance therewith. The optimum or preferred method to be used in any particular case will vary with the material being treated and with the form and purity thereof. The amount and character of the reagents used will also depend upon these factors and upon the procedure to be employed in the further purification and separation of the metals in the material being treated. The examples herein cited, therefore, are not intended to represent the only methods of operation that may be employed or even the best methods to be used in every case.

In general, the process contemplates the treatment of alloys or other materials .at high temperatures with a strong alkali such as caustic soda or caustic potash in the presence of an oxidizing agent such as a nitrate, nitrite, chromate, di-chromate or lead oxide.

Ordinarily I, prefer to carry the reaction to a final temperature of about 250 C. to 300 C. However, this. range of temperature is not critical and, in fact, the process may be successfully practiced by carrying the treatment to a final temperature above 125 C. No advantage is obtained when the temperature is carried as high as the melting point of the material being treated and, therefore, this is usually avoided and the upper limit of the temperature usually does not exceed about 400 C. In some instances the reaction is started at a temperature below 125 0., especially when water is present, but the treatment iscontinued at higher temperatures in order that'the reaction may be completed and satisfactory metal recovery attained. Substantially all water present or introduced with the reagents or material treated is driven off or decomposed during the reaction so that a dry or -substanti: a.lly dry reaction mass is produced.

The tin and other metals are then recovered from the reaction mass by leaching, or otherwise, as desired.

The alkali and oxidizing agent may be in a dry, finely divided state, or in a molten form, or they may be in the form of a solution. While the use of a solution has the advantage of bringing the reagents into intimate contact with the material being treated and, therefore, frequently aids in effecting complete reaction, it is desirable that the arnount'of water present or added should not be greater than that which will be readily driven oil or decomposed in the course of the treatment.

The use of a solution is also of convenience when the process is carried out in a cyclic manner since a concentrated leach liquor obtained from the treatment of the reaction mass of a previous operation may be used. The leach liquor ordinarily has the tin removed therefrom before re-use, while lead, antimony, and arsenic may be allowed to build up in the liquor, or they may be separated therefrom before it is recycled. In either case the alkali content of the liquor should be raised by concentration or the addition of more alkali to the liquor before it is employed so that the amount of water added will be insufiicient to prevent the formation of a dry or substantially dry reaction mass. When an excess of the alkali is used, the resulting reaction product may have a somewhat pasty consistency but otherwise the reaction mass will be substantially dry even when the alkali and oxidizing agent are used in the form of a solution.

The amount of alkali used in the process depends largely upon the amount of tin present in the material being treated and should be at least suflicient to combine with the tin oxide formed to convert it to sodium stannate. However, when, as is usual, the recovery of lead, antimony and arsenic is effected in the sameoperation, the amount of alkali to be used is also dependent upon the amount of these metals present. Moreover, an excess of the alkali is desirable in order that sodium stannate and lead oxide will dissolve and remain in solution when the reaction mass is leached with water.

When the amount of tin in the material being treated is low, or there is no tin at all, the amount of alkali used in effecting recovery of other metals is determined by the amount of the other metals to be recovered from the material being treated.

The amount of the oxidizing agent used depends upon whether a nitrate, nitrite, chromate or other agent is used and upon the amount of tin and other oxidizable metals to be extracted that are in the material treated. In general the amount of the oxidizing agent used should be at least sufficient to oxidize all of the tin and other metals to be recovered and, while an excess of the oxidizing agent does not interfere with the reaction, these reagents are relatively expensive and it is sometimes objectionable to have an unreacted oxidizing agent in the final reaction mass, particularly when electrolytic purification of the liquor is subsequently employed.

In order that my invention may be more clearly understood, the following examples are cited as illustrating the use of various amounts and types of reagents and as applied to the treatment of different types of tin and lead bearing materials.

Example N0. 1

A white matte having approximately the following composition was treated as indicated below:

Fer cent C 38.6 Sn 37.5 Pb 13.3 Sb 3.8 As A .04: Fe I .80 Ni :7 .54 S .94

Two hundred parts by weight of the alloy pulverized to pass a 200 mesh screen were added to a molten mixture of 600 parts by weight of caustic soda and 200 parts by weight of sodium tional 4% of the tin.

Example No. 2

When sodium nitrate was substituted for the sodium nitrite employed in Example No. 1 the reaction was substantially the same in character and the recovery of the tin amounted to 92% of the total tin present in the alloy.

Example No. 3

In another case wherein a solution of the alkali and oxidizing agent was used, the alloy treated had the following composition:

Per cent Cu 44.8 Sn 29.6 Sb 12.8 Pb 1 9.0 Other metals 4.4

Seven thousand parts of caustic soda and 4000 parts of sodium nitrite were mixed with 1000 parts of water and to this were added 7000 parts of the pulverized alloy. The mixture was agitated and brought to a final temperature of 280 C. where it was held for three hours. The reaction mass was dissolved in water. Ninety per cent of the tin originally present in the alloy were found in this water solution.

Example No. 4

A tin bearing wet slime was employed having the following major constituents:

Per cent Sn 29. 8 Sb 14. 2 Pb 6. 7 As 5. 7 Bi 3. 3 Cu 1. 6 S, Se, Te 7 Insoluble l. 2

625 parts by weight of this material was mixed with sufficient water to make a thin slurry and 200 parts by weight of flake caustic soda and 100 parts of sodium nitrate were added thereto. The material was heated to a final temperature of 280 C., producing a dry reaction mass which was leached with water. The recovery of tin in this case amounted to 78% of the tin present in the material treated.

Example No. 5

When using sodium di-chromate in the process, an alloy having the following composition was treated:

Per cent Cu 39. 9 Sn 35. Pb 14.1 As 6. 6 Sb 1. 2

Four hundred parts of sodium di-chromate and 400 parts of caustic soda were dissolved in 300 parts of water and 400 parts of the alloy were stirred into this mixture. The temperature was then brought up to 280 C. for one hour. On leaching with water, 60% of the tin was recovered.

Example N0. 6

Five hundred parts of lead oxide (litharge) were substituted for the sodium nitrate of Example No. 4 and the process carried out in the same manner. The tin recovery in this case amounted to 55% of that present in the alloy.

The products leached from the reaction mass may be variously treated to recover, separate, or purify the same as desired, or the leach liquor may be used directly in other processes. A typical method of treating the leach liquor suitable for the recovery and purification of tin is described in the patent to William T. Little, No. 1,787,078, dated December 30, 1930. However, other methods of treating the leach liquor or for separating tin or other metals therefrom may be employed as desired or necessary to attain the results without departing from my invention.- The leach liquor containing large amounts of caustic may be recycled and used as in Example No. 3 above, or may be otherwise used.

The invention may obviously be employed in the treatment of various types of materials other than those cited by way of illustration above and the temperature at which the process may be carried out may be either higher or lower than those indicated therein. I may also employ mixtures of oxidizing agents such as a mixture of sodium nitrate and lead oxide or other combinations of oxidizing agents in the practice of the process. Such variations in the practice of my invention will ordinarily be made in adapting the invention for use with any particular alloy or material being treated and in using difierent types of reagents. It should therefore be understood that the foregoing examples of methods of procedure in accordance with my invention are cited for purposes of illustration and are not intended to limit the scope of my invention.

By "alkali nitrate as used herein is meant sodium nitrate or its chemical equivalents, in; cluding potassium nitrate.

What is claimed is:

1. A method for the separation of tin and lead from materials containing the same, which compr ses the steps of mixing the materialwith a caustic alkali and an alkali nitrate and heating the mixture at atmospheric pressure to a temperature above about 125 C. and below the melting point of the materials under treatment, whereby the tin and lead present will be converted in o water soluble form.

2. A method for the separation of tin and lead from materials containing the same, which com prises the steps of mixing the material with a caustic alkali and an alkali nitrate and heating the mixture at atmospheric pressure to a final temperature between the limits of about 250 C. to 300 0., whereby the tin and lead present will be converted into water soluble form.

3. A method for the separation of tin and lead from materials containing the same, which comprises the steps of mixing the material with a caustic alkali and sodium nitrate and heating the mixture at atmospheric pressure to a temperature above about 125 C. and below the melting point of the materials under treatment, whereby the tin and lead present will be converted into Water soluble form.

4. A method for the separation of tin and lead from materials containing the same, which comprises the steps of mixing the material with a ca; stic alkali and sodium nitrate and heating the mixture at atmospheric pressure to a final temperature between the limits of about 250 C. to 300 C., whereby the tin and lead present will be converted into water soluble form.

5. In a process for the separation of tin and lead from materials containing the same, the process steps comprising heating the material at atmospheric pressure with a solution of a caustic and an alkali nitrate at a temperature above about 125 C. and below the melting point of the material under treatment and continuing the reaction until substantially all water present has been eliminated and a dryreaction mass is produced containing the tin and lead originally present in water soluble form. I

6. A method of separating tin and lead from materials containing the same, comprising the steps of mixing the material with a solution of a caustic alkali and an alkali nitrate, heating the mixture at atmospheric pressure to a temperature above about 125 C. and continuing the heating and the reaction until substantially all water has been eliminated and a dry reaction mass is produced containing the tin and lead originally present in water soluble form.

'7. A method of separating tin and lead from materials containing the same, comprising the steps of mixing the material with a solution of a caustic alkali and sodium nitrate, heating the mixture at atmospheric pressure to a tempera ture above about 125 C, and continuing the heating and the reaction until substantially all water has been eliminated and a dry reaction mass is produced containing the tin and lead originally present in water soluble form.

8. A method of separating tin and lead from alloys containing the same, comprising the steps of pulverizing the alloy, mixing the same with a caustic alkali and sodium nitrate, heating the mixture at atmospheric pressure to a temperature above about 125 C. while agitating and continuing the heating and the reaction untihsubstantially all water has been eliminated and a dry reaction mass is produced containing the tin and lead originally present in water soluble form.

9. A method of recovering metals such as tin, lead, antimony and arsenic from material containing the same, comprising the step of heating a dry mixture of the material with a caustic alkali and an oxidizing agent to a temperature above about 125 C. and below about 400 C.

10. A method of recovering metals such as tin, lead, antimony and arsenic from material containing the same, comprising the step of heating a dry mixture of the material with a caustic alkali and an oxidizing agent selected from the group consisting of a nitrate, nitrite, chromate,

di-chrornate, and lead oxide, to a temperature above about 125 C. and below about 400 C.

11. A method of recovering metals such as tin, lead, antimony and arsenic from material containing the same, comprising the step of heating a dry mixture of the material with a caustic alkali and sodium nitrate to a temperature above about 125 C. and below about 400 C.

12. A method for the recovery of metals such as tin, lead, antimony and arsenic from alloys containing the same, which comprises the step of pulverizing the alloy and mixing and agitating the same with a dry caustic alkali and a dry oxidizing agent selected from the group consisting of sodium nitrate, nitrite, chromate, or di-' chromate and lead oxide, while heating the mixture.

13. A method of producing a copper concentrate for electrolytic purification from an anti mony and'copper containing material which con:- prises the steps of treating the material, with a caustic alkali and sodium nitrate at a temperature in the neighborhood of 250 C. to 308 6., and leaching the reaction product with Water.

14. A method for the separation of tin and other readily oxidizable metals including lead, antimony and arsenic, from materials containing one or more of said metals, which comprises the steps of heating the material at atmospheric pressure with a caustic alkali and an alkali nitrate to a temperature above about 125 C. and below the melting point of the material under treatment, whereby the tin and any other of said metals present will be converted into soluble form, and leaching the resulting reaction product.

15. A method for the separation of tin and other readily oxidizable metals including lead, antimony and arsenic, from materials containing one or more of said metals, which comprises the steps of heating the material at atmospheric pressure with a caustic alkali and sodium nitrate to a temperature above 125 C. and below the melting point of the material under treatment, whereby the tin and any other of said metals present will be converted into soluble form, and leaching the resulting reaction product.

HARTMUT W. RICHTER. 

